Fluorocopolymer and fluororesin composition lowly permeable to liquid chemical

ABSTRACT

To provide a novel PFA-based fluorine-containing copolymer having improved impermeability to liquid chemicals while retaining the excellent heat resistance, stress cracking resistance and processability inherent in PFA-based fluororesins, a material and a molded article useful in the field of semiconductor production apparatus and the like, using the copolymer. The present invention provides a fluorine-containing copolymer comprising 90 to 99.4% by mole of a repeating unit derived from tetrafluoroethylene, 0.5 to 5% by mole of a repeating unit derived from at least one lower perfluoro(alkyl vinyl ether) represented by the formula (1): 
     
       
         CF 2 ═CF—O—Rf 1   (1) 
       
     
     in which Rf 1  is a perfluoroalkyl group having 2 to 4 carbon atoms, and 0.1 to 5% by mole of a repeating unit derived from at least one higher perfluoro(vinyl ether) represented by the formula (2): 
     
       
         CF 2 ═CF—O—Rf 2   (2) 
       
     
     in which Rf 2  is a perfluoroalkyl group having 5 to 10 carbon atoms or a perfluoro(alkoxy alkyl) group having 4 to 17 carbon atoms, wherein the fluorine-containing copolymer has a melt flow rate of 0.1 g/10 minutes to 100 g/10 minutes and melting point of 290° to 325° C., and a resin composition using the same.

TECHNICAL FIELD

The present invention relates to a novel fluorine-containing copolymer,a fluorine-containing resin composition which has excellentimpermeability to liquid chemicals and a molded article using the same

BACKGROUND ART

In the field of producing semi-conductors, a large amount of liquidchemicals and water have been conventionally used in wet processes. Afluorine-containing resin having excellent chemical resistance, heatresistance and melt moldability is used for pipes transporting suchliquid chemicals. Among fluorine-containing resins, a copolymer (PFA) oftetrafluoroethylene (TFE) and perfluoro(alkyl vinyl ether) (PAVE),particularly a copolymer of perfluoro(propyl vinyl ether) (PPVE), isexcellent in chemical resistance, heat resistance, melt-moldability andstress cracking resistance, and thus preferably used for pipingarrangements such as tubes and joints for transporting liquid chemicals.

However, these PFA piping arrangements have a problem of chemical liquidpermeation in a small amount and needs some improvement. In currentsemiconductor production plants, there are some countermeasures such ascovering the outside of a PFA tube with a pipe made of poly(vinylchloride) (PVC) to make a double piping structure, or in the wet stationarea, exchanging PFA tubes regularly, wrapping them by a PVC film orfurther wiping the outside of a tube with a cloth.

These measures increase equipment and maintenance costs as might beexpected, resulting in the increase of the cost for producingsemiconductors.

As mentioned above, it is now practically difficult to solve the liquidchemical permeation problem of PFA in view of structure and maintenance,and therefore improvements are investigated with respect to itsmaterials.

For example, there is a measure to use a fluorine-containing resin moreimpermeable to liquid chemicals, and among the fluorine-containingresins, it is effective to choose poly(chlorotrifluoroethylene) which isthe most impermeable to liquid chemicals. However, this resin has aproblem that it is poor in stress cracking resistance, moldability andheat resistance.

Furthermore, there is a way to increase crystallinity of PFA. It iseffective to increase crystallinity since permeation of liquid chemicalis generally observed at amorphous parts. As to PFA, it is possible toincrease the crystallinity by decreasing the amount of perfluoro(alkylvinyl ether) (PAVE). In this case, however, there arise defects thatprocessability and crack resistance are decreased.

In addition, Japanese Unexamined Patent Publication No. 259216/1998discloses the improvement of impermeability to liquid chemicals bymodifying PFA using, as a third component, fluorovinyl ether whichcontains a reactive group such as a hydroxyl group. However, chemicalresistance is decreased on the contrary since the terminal group of themodifying monomer is a reactive group represented by —CH₂OH. Further,permeability to liquid chemicals are evaluated only in terms of weightincrease after immersing the material in fuming sulfuric acid for fourweeks at room temperature, and there is no substantial description ofthe permeation amount of liquid chemical in the publication.

On the other hand, Japanese Unexamined Patent Publication No.116706/1999 discloses a process for irradiating a molded article of afluorine-containing resin such as PFA or a copolymer (FEP) oftetrafluoroethylene and hexafluoropropylene with ionizing radiationunder inert gas atmosphere and at temperature of at least the meltingpoint to cross-link the polymers, thereby improving gas barrierproperty. However, special apparatus is required for such treatment, andthis is not preferable from an economical point of view.

An object of the present invention is to provide a melt-moldablefluorine-containing copolymer which can provide, in an economicallyefficient manner, a molded article having excellent impermeability toliquid chemicals while retaining the excellent heat resistance, stressresistance and processability inherent in PFA-based fluororesins, afluorine-containing resin composition and a molded article using thesame.

As a result of intensive studies, it has been found that chemicalimpermeability can be improved without losing inherent properties of aresin by modifying a tetrafluoroethylene copolymer using a particularperfluoro(alkyl vinyl ether) and the present invention has beencompleted.

DISCLOSURE OF INVENTION

The present invention relates to a fluorine-containing copolymercomprising 90 to 99.4% by mole of a repeating unit derived fromtetrafluoroethylene, 0.5 to 5% by mole of a repeating unit derived fromat least one lower perfluoro(alkyl vinyl ether) represented by theformula (1):

CF₂═CF—O—Rf¹  (1)

in which Rf¹ is a perfluoroalkyl group having 2 to 4 carbon atoms, and0.1 to 5% by mole of a repeating unit derived from at least one higherperfluoro(vinyl ether) represented by the formula (2):

CF₂═CF—O—Rf²  (2)

in which Rf² is a perfluoroalkyl group having 5 to 10 carbon atoms or aperfluoro(alkoxy alkyl) group having 4 to 17 carbon atoms, wherein thefluorine-containing copolymer has a melt flow rate of 0.1 g/10 minutesto 100 g/10 minutes and a melting point of 290° to 325° C.

It is preferable that Rf² in the higher fluoro(vinyl ether) representedby the formula (2) is a perfluoroalkoxyl group represented by theformula (3):

—(CF₂C(CF₃)FO)_(n)—Rf³  (3)

in which n is an integer of 1 to 4 and Rf³ is a perfluoroalkyl grouphaving 1 to 5 carbon atoms.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a schematic side view of the testing machine used forinvestigating liquid chemical permeability of the molded article of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The novel copolymer of the present invention is a terpolymer comprisingTFE, lower perfluro(alkyl vinyl ether) represented by the formula (1)and higher perfluoro(vinyl ether) represented by the formula (2).

Examples of lower perfluro(alkyl vinyl ether) represented by the formula(1) include perfluoro(ethyl vinyl ether), perfluoro(propyl vinyl ether),perfluoro(butyl vinyl ether) and the like. Among these, perfluoro(propylvinyl ether) (PPVE) is preferable.

Examples of higher perfluro(alkyl vinyl ether) represented by theformula (2) include perfluoro(pentyl vinyl ether), perfluoro(hexyl vinylether), perfluoro(heptyl vinyl ether) and the like.

Further, as higher fluoro(alkoxy alkyl vinyl ether) represented by theformula (2), perfluoroalkoxyl group is preferable, whose Rf² isrepresented by the formula (3):

—(CF₂C(CF₃)FO)_(n)—Rf³  (3)

in which n is an integer of 1 to 4 and Rf³ is a perfluoroalkyl grouphaving 1 to 5 carbon atoms. Concrete examples thereof are

CF₂═CFO—(CF₂C(CF₃)FO)—CF₃,

CF₂═CFO—(CF₂C(CF₃)FO)₂—CF₃,

CF₂═CFO—(CF₂C(CF₃)FO)₃—CF₃,

CF₂═CFO—(CF₂C(CF₃)FO)—CF₂CF₃,

CF₂═CFO—(CF₂C(CF₃)FO)₂—CF₂CF₃,

CF₂═CFO—(CF₂C(CF₃)FO)₃—CF₂CF₃,

CF₂═CFO—(CF₂C(CF₃)FO)—CF₂CF₂CF₃,

CF₂═CFO—(CF₂C(CF₃)FO)₂—CF₂CF₂CF₃,

CF₂═CFO—(CF₂C(CF₃)FO)₃—CF₂CF₂CF₃, and the like.

Among these, CF₂═CFO—(CF₂C(CF₃)FO)—CF₂CF₂CF₃,CF₂═CFO—(CF₂C(CF₃)FO)₂—CF₂CF₂CF₃ and CF₂═CFO—(CF₂C(CF₃)FO)₃—CF₂CF₂CF₃are particularly preferable.

The composition among TFE, perfluro(alkyl vinyl ether) (1) having ashort side chain represented by the formula (1) and perfluro(vinylether) (2) having a long side chain represented by the formula (2),namely TFE/(1)/(2), is 90 to 99.4/0.5 to 5/0.1 to 5 (% by mole),preferably 94 to 99.4/0.5 to 3.0/0.1 to 3.0 (% by mole).

When the unit of lower vinyl ether (1) is more than 5% by mole, heatresistance is decreased because crystallinity is decreased. When theunit of lower vinyl ether (1) is less than 0.5% by mole,melt-moldability and stress cracking resistance are decreased.

When the unit of higher vinyl ether (2) is more than 5% by mole,prevention effect on permeation is decreased because crystallinity isdecreased. When the unit of higher vinyl ether (2) is less than 0.1% bymole, the prevention effect on permeation is insufficient becausemodification is too small.

Examples of suitable copolymers having a particularly excellentprevention effect on permeation are TFE/perfluoro(propyl vinylether)/CF₂═CFO—(CF₂C(CF₃)FO)—CF₂CF₂CF₃ (90 to 99.4/0.5 to 5/0.1 to 5),TFE/perfluoro(propyl vinyl ether)/CF₂═CFO—(CF₂C(CF₃)FO)₂—CF₂CF₂CF₃ (90to 99.4/0.5 to 5/0.1 to 5), and TFE/perfluoro(propyl vinylether)/CF₂═CFO—(CF₂C(CF₃)FO)₃—CF₂CF₂CF₃ (90 to 99.4/0.5 to 5/0.1 to 5),but not particularly limited thereto.

Although some prior arts describe that at least two kinds ofperfluoro(vinyl ether) may be used as copolymerization components forTFE (for example, Japanese Examined Patent Publication No. 83/1992 andJapanese Unexamined Patent Publication No. 304832/1995), there is noconcrete example of copolymerizing particular perfluoro(vinyl ether) ofthe present invention, namely, lower perfluoro(alkyl vinyl ether) (1)with higher perfluoro(vinyl ether) (2) in a particular ratio. Further,it is not known that the fluorine-containing copolymer of the presentinvention has a specific effect such as excellent liquid chemicalimpermeability.

The fluorine-containing copolymer of the present invention has a meltingpoint of 290° to 325° C. and a melt flow rate of 0.1 to 100 g/10minutes, preferably 0.5 to 30 g/10 minutes. In particular, when thecopolymer is molded into a tube, the melt flow rate is preferably 1 to 3g/10 minutes in view of excellent stress cracking resistance andmelt-moldability.

The polymerization process for obtaining the fluorine-containingcopolymer of the present invention is not particularly limited. It ispossible to obtain the copolymer under usual polymerization conditionsemploying emulsion polymerization, suspension polymerization, solutionpolymerization or bulk polymerization which are known to the personskilled in the art.

According to the present invention, it is possible to prepare a moldedarticle whose permeability to liquid chemicals is inhibited.Specifically, a molded article is obtained, whose permeation amount ofnitric acid is at most 2.0×10⁻⁶ g.cm/cm², preferably at most 1.6×10⁻⁶g.cm/cm² after 40 days in a liquid chemical permeation test as mentionedbelow. That is, the present invention also relates to a molded articleobtained by molding the fluorine-containing copolymer.

In addition, it is possible to obtain a molded article having furtherreduced nitric acid permeation by molding a fluorine-containing resincomposition obtained by adding a liquid chemical permeation inhibitor tothe fluorine-containing copolymer of the present invention.

The present invention therefore relates to a fluorine-containing resincomposition comprising a fluorine-containing copolymer and a liquidchemical permeation inhibitor mentioned above.

The liquid chemical permeation inhibitor used in the present inventionmeans an amorphous fluorine-containing copolymer or afluorine-containing multi-segmented polymer comprising an amorphousfluorine-containing polymer chain segment.

Herein, “amorphous” means that the polymer has neither melting peaktemperature (in case of temperature increase, Tm) nor crystallizationpeak temperature (in case of temperature decrease, Tc), but glasstransition temperature (Tg) when measurement is carried out using adifferential scanning calorimeter (DSC). In other words, there issubstantially no crystallized area. On the other hand, “crystalline”means that the polymer has both Tm and Tc.

Additionally, the “amorphous” segment (A) and the “crystalline” segment(B) in the fluorine-containing multi-segmented polymer means a polymerwhich comprises the same repeating unit as that of each segment andsatisfies the above definitions of “amorphous” or “crystalline”.

The amorphous fluorine-containing polymer and the amorphousfluorine-containing polymer chain segment (A) of the fluorine-containingmulti-segmented polymer as the liquid chemical permeation inhibitorsused in the present invention, have a glass transition temperature (Tg).An amorphous polymer whose Tg is at most room temperature (25° C.) isreferred to as an “elastomer”, while those whose Tg is higher than 25°C. is referred to as a “resin”. The elastomer with Tg of at most 25° C.is preferable in view of its high prevention effect on liquid chemicalpermeation and is suitably selected depending on the compatibility withthe crystalline PFA to be used. However, the amorphousfluorine-containing polymer and the amorphous fluorine-containingpolymer chain segment (A) used in the present invention may be anelastomer with Tg of at most 25° C. or a resin with Tg higher than 25°C.

The liquid chemical permeation inhibitor of the present invention meansthose comprising an amorphous fluorine-containing polymer or thosecomprising a fluorine-containing multi-segmented polymer. At first, theamorphous fluorine-containing polymer is explained.

The amorphous fluorine-containing polymer includes a fluorine-containingelastomer whose Tg is at most 25° C. and an amorphousfluorine-containing polymer resin whose Tg is higher than 25° C.

Examples of the fluorine-containing elastomer are a perfluoro elastomersuch as tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer; anda fluorine-containing elastomer having hydrogen atom such as avinylidenefluoride-hexafluoropropylene copolymer, avinylidenefluoride-hexafluoropropylene-tetrafluoroethylene copolymer, avinylidenefluoride-chlorotrifluoroethylene copolymer or avinylidenefluoride-chlorotrifluoroethylene-tetrafluoroethylenecopolymer.

Among these, the TFE-PAVE copolymer is preferable as a liquid chemicalpermeation inhibitor for PFA from the viewpoint of the compatibilitywith PFA. Examples of perfluro(alkyl vinyl ether) (PAVE) for theTFE-PAVE copolymer are perfluofo(methyl vinyl ether), perfluofo(ethylvinyl ether), perfluofo(propyl vinyl ether) and the like. The amount ofPAVE is 10 to 50% by mole, preferably 20 to 50% by mole, where theTFE-PAVE copolymer has neither Tm nor Tc. Though the border betweenamorphousness and crystallinity of the copolymer lies in the range of 10to 20% by mole, the TFE-PAVE copolymer can be used as the liquidchemical permeation inhibitor as long as it is amorphous.

The fluorine-containing elastomer can be prepared by a knownpolymerization process which is a process for preparing a fluorinerubber (U.S. Pat. No. 4,158,678 and U.S. Pat. No. 5,001,278).

For example, there is a process of carrying out emulsion polymerizationunder substantially no oxygen condition in an aqueous medium in thepresence of an iodine compound, preferably a diiodine compound, withstirring under pressure using a radical polymerization initiator.

Typical examples of the diiodine compound are1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane,1,3-diiodo-2-chloroperfluoropropane,1,5-diiodo-2,4-dichloroperfluoropentane, 1,6-diiodoperfluorohexane,1,8-diiodoperfluorooctane, 1,12-diiodoperfluorododecane,1,16-diiodoperfluorohexadecane, diiodomethane and 1,2-diiodoethane.These compounds can be used alone or in combination thereof. Amongthese, 1,4-diiodoperfluorobutane is preferable. The amount of thediiodine compound is 0.01 to 1% by weight based on the total weight ofthe fluorine-containing monomer.

In addition, fluorine-containing elastomer may be prepared bycopolymerizing an iodine-containing monomer in the present invention. Asthe iodine-containing monomer, perfluoro(vinyl ether) compounds arepreferable in view of copolymerizability. For example,perfluoro(6,6dihydro-6-iodo-3-oxa-1-hexene) orperfluoro(5-iodo-3-oxa-1-pentene) is preferable as disclosed in JapaneseExamined Patent Publication No. 63482/1993 and Japanese UnexaminedPatent Publication No. 12734/1987.

The polymerization temperature is from about 10° to about 100° C.depending on properties of the initiator or kinds of monomers to beused. However, when the temperature is lower than 40° C., polymerizationrate is low in case of using persulfate alone. Even in case of using aredox initiator to which sulfite salts or the like is added,polymerization rate is low and metal ion in the reducing agent remainsin the polymer, which is not preferable for semiconductor production orthe like.

The radical initiator to be used may be the same as conventionalinitiators employed for polymerization of a fluorine-containingelastomer. Examples of these initiators are organic or inorganicperoxides and azo compounds. Typical initiators are persulfates,carbonate peroxides, peroxide esters and the like, and a preferableinitiator includes ammonium persulfate (APS). APS may be used alone orin combination with a reducing agent such as sulfites or sulfite salts.However, when cleanness is required, it is not recommended to use suchreducing agents, which may generate metal ions.

As to the emulsifier used for emulsion polymerization, a wide variety ofemulsifiers can be used, and fluorocarbon chain or fluoro polyetherchain-containing carboxylate salts are preferable from the viewpoint ofinhibiting the chain transfer reaction to emulsifier molecules duringpolymerization. The amount of emulsifier is preferably about 0.05 to 2%by weight, more preferably 0.2 to 1.5% by weight.

The polymerization pressure can be extensively changed, ranging from 0.5to 5 MPa in general. The higher the polymerization pressure is, thehigher the polymerization rate is, and therefore, the polymerizationpressure is preferably at least 0.8 MPa from the viewpoint of improvingproductivity.

It is preferable to adjust the number average molecular weight of thethus-obtained fluorine-containing elastomer to 5,000 to 750,000,particularly 20,000 to 400,000, further particularly 50,000 to 400,000since excellent mixing with the crystalline fluorine-containing resin isachieved.

The amorphous fluorine-containing polymer resin having Tg of higher than25° C. includes an amorphous fluorine-containing polymer containing acyclic structure in the main chain. Examples thereof are atetrafluoroethylene-fluorodioxol copolymer (such astetrafluoroethylene-fluoro-2,2-dimethyl-1,3-dioxol copolymer and thelike as in Japanese Examined Patent Publication No. 18964/1988); or anamorphous fluorine-containing polymer which has a fluorine-containingaliphatic ring in the main chain and which is obtained by cyclicpolymerization of a fluorine-containing monomer having at least twopolymerizable double bonds, (for example, polymers obtained by cyclicpolymerization of a perfluoro monomer such as perfluoro(allyl vinylether) and perfluoro(butenyl vinyl ether); or a copolymer of suchperfluoro monomers and a radically polymerizable monomer includingtetrafluoroethylene, chlorotrifluoroethylene or perfluoro(alkyl vinylether). Among these, perfluoro amorphous polymers such as atetrafluoroethylene-perfluoro-2,2-dimethyl-1,3-dioxol copolymer and aperfluoro(allyl vinyl ether) copolymer are preferable from theviewpoints of heat resistance and chemical resistance.

Secondly, the fluorine-containing multi-segmented polymer is explained.

The fluorine-containing multi-segmented polymer used as the liquidchemical permeation inhibitor in the present invention comprises anamorphous fluorine-containing polymer chain segment (A) and acrystalline fluorine-containing polymer chain segment (B).

As the amorphous fluorine-containing polymer chain segment (A), thereare an elastomeric one and a resin one as is the case with the aboveamorphous fluorine-containing polymer.

The elastomeric fluorine-containing polymer chain segment (A) is asegment whose Tg is at most 25° C. Examples thereof are the abovecopolymers listed as the fluorine-containing elastomer and this segmentcan be prepared by the iodine transfer polymerization mentioned above.When prepared by the iodine transfer polymerization, the segment has aperhalo terminal containing iodine atom, which can serve as a startingpoint for block copolymerization of the crystalline fluorine-containingpolymer chain segment (B).

It is preferable to adjust the number average molecular weight ofelastomeric fluorine-containing polymer chain segment (A) to 5,000 to750,000, particularly 20,000 to 400,000, further particularly 50,000 to400,000.

Particularly preferable examples of the elastomeric fluorine-containingpolymer chain segment (A) include an elastomeric TFE-PAVE segmentcomprising a repeating unit derived from tetrafluoroethylene (TFE) and arepeating unit derived from perfluoro(alkyl vinyl ether). In this case,the amount of the PAVE repeating unit is such that the segment has Tg ofat most 25° C. and does not have Tm and Tc, that is, 10 to 50% by mole,preferably 20 to 50% by mole. Though the border between amorphousnessand crystallinity of the segment lies in the range of 10 to 20% by mole,those segments in the amorphous range should be used.

The crystalline fluorine-containing polymer chain segment (B) of thefluorine-containing multi-segmented polymer used in the presentinvention serves as an anchor when mixed with a crystallinefluorine-containing resin which is the matrix, in order to prevent theamorphous segment (A) from falling out from the matrix resin in the formof particles. Therefore, a segment compatible to the crystallinefluorine-containing resin is selected as the crystalline segment (B).Specifically, a segment comprising a repeating unit derived fromtetrafluoroethylene (TFE) and a repeating unit represented by theformula (6):

CF₂═CF—Rf⁴  (6)

in which Rf⁴ represents CF₃ or ORf⁵ (Rf⁵ being a perfluoroalkyl grouphaving 1 to 5 carbon atoms), and the amount of the repeating unitrepresented by the formula (6) is at most 20% by mole, preferably 0 to10% by mole, more preferably 0 to 4% by mole. When the amount of therepeating unit represented by the formula (6) is more than 20% by mole,it is not preferable since the segment becomes amorphous and theanchoring effect becomes insufficient. Though the border betweenamorphousness and crystallinity of the segment lies in the range of 10to 20% by mole, those segments in the crystalline range should be used.

Concrete examples of the monomer represented by the formula (6) includehexafluoropropylene (HFP), perfluoro(alkyl vinyl ether) (PAVE) and thelike. Examples of PAVE are perfluoro(methyl vinyl ether) (PMVE),perfluoro(ethyl vinyl ether) (PEVE), perfluoro(propyl vinyl ether)(PPVE) and the like. Among these, PPVE is preferable from the viewpointof its excellent compatibility with PFA.

Particularly preferable examples of the crystalline segment (B) includea PTFE segment essentially consisting of a repeating unit derived fromTFE or a crystalline PFA segment.

The block copolymerization of the crystalline segment (B) with theamorphous segment (A) is carried out following the emulsionpolymerization to obtain the amorphous segment (A), using monomers forthe crystalline segment (B). The number average molecular weight of thecrystalline segment (B) can be extensively adjusted to 1,000 to1,200,000, preferably 3,000 to 400,000, more preferably 10,000 to400,000.

The thus-obtained fluorine-containing multi-segmented polymer comprisesa polymer (B—A—B) in which crystalline segments (B) are bound to bothsides of the amorphous segment (A), and a polymer (A—B) in which acrystalline segment (B) is bound to one side of the amorphous segment(A), as a main segment.

In the present invention, the ratio of the amorphous segment (A) to thecrystalline segment (B) is suitably adjusted within the above molecularweight range, but, for example, (A)/(B) is 10/90 to 99/1, preferably25/75 to 95/5 in a weight ratio. The molecular weight of thefluorine-containing multi-segmented polymer is those which achieveexcellent mixing with the crystalline fluorine-containing resin.

More specifically, combination of the following segments is available.

(1) The amorphous segment (A) is TFE-PMVE (80/20 to 50/50 in molarratio) having a number average molecular weight of 50,000 to 400,000;

the crystalline segment (B) is TFE-PPVE (100/0 to 80/20 in molar ratio)having a number average molecular weight of 10,000 to 400,000; and

segmented polymer structure: B—A—B.

This segmented polymer makes PFA sphaerites minute, has an anchoringeffect, and is excellent in inhibiting liquid chemical permeationwithout lowering PFA properties.

By compounding these liquid chemical permeation inhibitors, thepermeation amount of nitric acid is reduced by at least 30%.

In addition, it is preferable to subject the liquid chemical permeationinhibitor to fluorine gas treatment in order to improve heat resistanceand for enhancing prevention effect on liquid chemical permeation of themolded article.

The fluorine gas treatment is carried out by contacting fluorine gaswith the liquid chemical permeation inhibitor. However, reaction withfluorine generates much heat, and therefore it is preferable to dilutethe fluorine gas with inert gas such as nitrogen gas. The amount offluorine in the gas mixture comprising fluorine gas and inert gas is 1to 100% by weight, preferably 10 to 25% by weight. The treatmenttemperature is 150° to 250° C., preferably 200° to 250° C., and thefluorine gas treatment time is 3 to 16 hours, preferably 4 to 12 hours.The pressure in the fluorine gas treatment ranges from 1 to 10 atm, butatmospheric pressure is preferable. In case of using the reactor underatmospheric pressure, the mixed gas of fluorine gas and inert gas iscontinuously passed through the reactor. As a result, unstable terminalsin the liquid chemical permeation inhibitor are converted to —CF₃terminals and then thermally stabilized. In addition, iodine bound tothe fluorine-containing elastomer and the fluorine-containingmulti-segmented polymer can be removed to the level as low as thedetection limit.

The amount of the liquid chemical permeation inhibitor is 0.1 to 50parts, preferably 0.25 to 20 parts by weight based on 100 parts byweight (hereinafter referred to as “part”) of the fluorine-containingcopolymer. When the amount of the liquid chemical permeation inhibitoris too large, there is a problem that mechanical strength is reduced.

As the molding process of the copolymer and the resin composition of thepresent invention, compression molding, transfer molding, extrusionmolding, injection molding and blow molding are available, as is thecase with conventional PFA.

Desired molded articles can be obtained according to such moldingprocesses, and examples of the molded article include a sheet, a film, apacking, a round bar, a square bar, a pipe, a tube, a round bath, asquare bath, a tank, a wafer carrier, a wafer box, a beaker, a filterhousing, a flow meter, a pump, a valve, a cock, a connector, a nut andthe like.

Among these, the molded article can be suitably used for tubes, pipes,tanks or connectors used for various chemical reaction apparatus,semiconductor production apparatus or liquid chemical feeders whereimpermeability to liquid chemical is particularly required.

Hereinafter, the present invention is explained in detail by means ofexamples, but is not limited thereto.

Firstly, measurements of each property were carried out according to thefollowing procedures:

(1) Composition Analysis

Compositions of each polymer are determined according to both of the¹⁹F-NMR method and the IR method.

(2) Thermal Decomposition Temperature

Thermal decomposition temperature means temperature (° C.) at which theweight of the polymer is decreased by 1.0% by weight at a temperatureincrease rate of 10° C./minute using a differential scanning calorimeter(RDC-220 made by Seiko Instruments Inc.).

(3) Melting Point

Melting point means a value (° C.) determined from the melting curvewhen temperature is increased at a temperature increase rate of 10°C./minute using a differential scanning calorimeter (RDC-220 made bySeiko Instruments Inc.).

(4) Melt Flow Rate (MFR)

Melt flow rate is a value (g/10 minutes) measured according to ASTM D2116 at 372° C. under a load of 5 kg using a melt indexer (made by ToyoSeiki K. K.).

(5) MIT Value (Flexibility Fatigue Resistance)

A test piece is cut from a compression-molded sheet having a thicknessof 0.20 to 0.23 mm, and measurement is carried out according to ASTMD2176 under the test conditions of a load of 12.15 N (1.25 kgf), abending rate of 178 times/minute and a bending angle of 135° using a MITflexibility fatigue resistance measuring machine (made by ToyoSeikiK.K.).

(6) Mechanical Strength

Mechanical strength is measured according to ASTM D 638 using a Tensilontensile tester (made by Shimadzu Corporation). A test piece is cut froma compression-molded sheet having a thickness of 1.0 mm.

(7) Liquid Chemical Permeation Test

A sheet having a thickness of 0.2 mm and a diameter of 120 mm φ isprepared by compresion-molding using a heat press at 350° C.

The sample sheet 1 is interposed between two glass containers 2 a and 2b (both having a capacity of 200 ml) by using fluorine rubber O-rings 3as shown in FIG. 1. This unit is placed in a thermostat adjusted to 25°C. with filling the container 2 a on one side of the sheet with 200 mlof 60% by weight nitric acid and the container 2 b on the other sidewith 200 ml of pure water (liquid contact area of the sample sheet 1 is70 mmφ). The unit is allowed to stand in this state and liquid issampled in an amount of about 1 ml from the sampling port 4 installed onthe container 2 b containing pure water after 40 days, and theconcentration of nitric acid ion in pure water (Yppm) is quantifiedusing an ion chromatograph (made by Yokogawa Electric Corporation,IC7000-E). The permeation amount of nitric acid is calculated based onthe following equation:

X=Y×200×0.02×10⁻⁶/(3.5×3.5×3.14)

EXAMPLE 1

An autoclave having an internal volume of 4.21 was charged with 100 mlof pure water. Then, after replacing the internal air with pure nitrogengas sufficiently, the autoclave was evacuated and charged with 800 g ofperfluoro(cyclo butane) as a solvent, 40 g of PPVE, 4 g ofCF₂═CFO—(CF₂C(CF₃)FO)₂—CF₂CF₂CF₃ (hereinafter referred to as n=2VE) and7.0 g of methanol. Stirring was carried out and the inside temperaturewas kept at 35° C. TFE is then pressed into the autoclave and the insidepressure of the autoclave was kept at 0.83 MPaG. As a polymerizationinitiator, 1.75 g of n-propylperoxy dicarbonate was added to start thereaction. Since the pressure decreases as the reaction proceeds,additional TFE was pressed thereinto to maintain the pressure at 0.83MPaG. Stirring was stopped when the charged amount of TFE reached 230 g,and unreacted monomers and the solvent were purged out. The white powdergenerated in the autoclave was washed with water and then CH₃CCl₂F(R-141b), and the powder was dried at 200° C. for 5 hours. An objectivefluorine-containing copolymer was obtained in an amount of 236 g.

Properties of the copolymer including the permeation amount of nitricacid are shown in Table. 1.

EXAMPLE 2

An objective fluorine-containing copolymer was obtained in an amount of245 g in the same manner as in Example 1 except for changing the amountsof n=2VE and methanol to 1.3 g and 2.0 g, respectively.

Properties of the copolymer including the permeation amount of nitricacid are shown in Table 1.

EXAMPLE 3

An objective fluorine-containing copolymer was obtained in an amount of237 g in the same manner as in Example 1 except for changing the amountsof PPVE, n=2VE and methanol to 20 g, 13 g and 2.0 g, respectively.

Properties of the copolymer including the permeation amount of nitricacid are shown in Table 1.

EXAMPLE 4

An objective fluorine-containing copolymer was obtained in an amount of245 g in the same manner as in Example 1 except for changing the amountsof PPVE and n=2VE to 30 g and 8 g, respectively.

Properties of the copolymer including the permeation amount of nitricacid are shown in Table 1.

EXAMPLE 5

An objective fluorine-containing copolymer was obtained in an amount of237 g in the same manner as in Example 1 except for changing the amountsof PPVE, n=2VE and methanol to 35 g, 34 g and 2.0 g, respectively.

Properties of the copolymer including the permeation amount of nitricacid are shown in Table 1.

EXAMPLE 6

An objective fluorine-containing copolymer was obtained in an amount of235 g in the same manner as in Example 1 except for changing the amountsof PPVE, n=2VE and methanol to 35 g, 34 g and 4.0 g, respectively.

Properties of the copolymer including the permeation amount of nitricacid are shown in Table 1.

EXAMPLE 7

(Synthesis of a Fluorine-containing Multi-segmented Polymer)

A stainless steel autoclave having an internal volume of 47 l wascharged with 30 l of pure water, 300 g of C₇F₁₅COONH₄ as an emulsifierand 300 g of disodium hydrogenphosphate 12 hydrate as a pH regulator.The internal air was replaced with nitrogen gas sufficiently and thenthe temperature was elevated to 50° C. with stirring at 200 rpm. A mixedgas of tetrafluoroethylene (TFE) and perfluoro(methyl vinyl ether)(PMVE) (TFE/PMVE=32/68 in a molar ratio) was added thereto so that theinside pressure became 0.78 MPaG. Then, 100 ml of an aqueous solutioncontaining 55.8 mg/ml of ammonium persulfate (APS) was pressed into theautoclave with nitrogen pressure to initiate the reaction.

When the inside pressure decreased to 0.69 MPaG with the progress of thepolymerization, a mixture of 27.24 g of a diiodine compound I(CF₂)₄I and234 g of an aqueous solution containing 10% by weight of C₇F₁₅COONH₄ waspressed into the autoclave with nitrogen pressure. Subsequently, 60 g ofTFE and 58 g of PMVE (TFE/PMVE=63/37 in a molar ratio) were pressedthereinto with self pressure and by a plunger pump, respectively, sothat the pressure was set to 0.78 MPaG. After that, TFE and PMVE werepressed thereinto similarly as the reaction proceeds, and pressure upand pressure down were repeated between 0.69 to 0.78 MPaG.

When the total amount of TFE and PMVE reached 6,000 g twelve hours afterthe start of the polymerization reaction, the autoclave was cooled,unreacted monomers were removed and an aqueous dispersion whose solidcontent concentration was 18.04% by weight was obtained.

Part of the aqueous dispersion was sampled, frozen and coagulated. Theaqueous dispersion was then thawed, and the coagulate was washed withwater and dried under vacuum to obtain an elastomeric amorphous polymer.The polymer had a Mooney viscosity ML₁₊₁₀ (100° C.) of 94 and a limitingviscosity [η] of 0.654 dl/g.

As a result of ¹⁹F-NMR analysis, the composition of monomer units of thepolymer was TFE/PMVE=60/40% by mole, and the polymer had a Tg (mediumvalue) of 2° C. according to DSC analysis.

A stainless steel autoclave having an internal volume of 3 l was chargedwith 349 g of the aqueous dispersion of the amorphous polymer obtainedabove, 685 g of pure water, 26.4 g of PPVE. The internal air wasreplaced with nitrogen gas sufficiently and the temperature wasmaintained at 80° C. With stirring at 400 rpm, TFE was pressed into theautoclave so that the inside pressure became 0.78 MPaG.

Thereafter, a solution obtained by dissolving 10 mg of ammoniumpersulfate into 2 ml of water was pressed into the autoclave by usingnitrogen and the reaction was started.

Since the pressure decreases as the polymerization reaction proceeds,re-pressurization was carried out to 0.78 MPaG when the pressuredecreased to 0.69 MPaG. Pressure up and pressure down were repeatedbetween 0.69 and 0.78 MPaG.

When the consumption of TFE amounted to 189 g from the start of thepolymerization, supply of TFE was stopped, the autoclave was cooled andunreacted monomers were removed to obtain 1231 g of a semitransparentaqueous dispersion.

The obtained aqueous dispersion had a solid content concentration of20.2% by weight and a particle diameter of 82.3 nm when measured by adynamic light scattering method.

Owing to the increase of the obtained amount of the polymers, thecalculated ratio of the crystalline fluorine-containing polymer chainsegment (B) to the total polymers, namely, {(polymer amount obtained atpost-polymerization)−(charged amount of polymers)}+(polymer amountobtained at post-polymerization), was 75% by weight.

The obtained aqueous dispersion was frozen and coagulated. Coagulatedpolymers were washed and dried, and white solid substance was obtained.

The composition of the crystalline fluorine-containing polymer chainsegment (B) in the obtained fluorine-containing multi-segmented polymerwas TFE/PPVE=97.1/2.9% by mole according to ¹⁹F-NMR analysis. Inaddition, according to DSC analysis, the amorphous fluorine-containingpolymer chain segment (A) had no Tm and Tc but Tg of 2° C. while thecrystalline fluorine-containing polymer chain segment (B) had Tm of312.7° C. and Tc of 294.3° C. The multi-segmented polymer had MFR of 11g/10 minutes.

(Preparation of Fluorine-containing Resin Composition)

A fluorine-containing resin composition was prepared by melt-kneading 1part of the liquid chemical permeation inhibitor comprising thefluorine-containing multi-segmented polymer produced above with 100parts of PFA synthesized in Example 6. Each component was put into aroller mixer type R-60H (mixer capacity: about 60 ml) made by Toyo SeikiK.K. and melt-kneading was carried out at 350° C. for 10 minutes at arotation speed of 15 rpm.

The obtained fluorine-containing resin composition was treated withfluorine in the following manner.

The fluorine-containing resin composition in a special tray was placedin a box-shaped reaction oven and the oven was sealed. Replacement withnitrogen gas was sufficiently carried out and a mixed gas of fluorinegas and nitrogen gas (concentration of fluorine gas: 20% by weight) waspassed at a flow rate of 0.6 l/minute for 5 hours. The inside of theoven was maintained at atmospheric pressure at 230° C.

After the reaction, heating was stopped and the mixed gas was changed tonitrogen gas to remove fluorine gas sufficiently over about 2 hours.

Properties of the fluorinated fluorine-containing resin compositionincluding nitric acid permeation amount are shown in Table 1.

Comparative Example 1

A TFE-PPVE copolymer in an amount of 235 g was obtained in the samemanner as in Example 1 except for charging no n=2VE.

Properties of the compolymer including nitric acid permeation amount areshown in Table 1.

TABLE 1 MIT Temperature at Permeation Composition of copolymer Melting(ten which weight is amount of liquid (composition) (% by mole) pointMFR thousand decreased by chemical TFE PPVE n = 2VE (° C.) (g/10minutes) times) 1% (° C.) (g · cm/cm²) Ex. 1 98.1 1.7 0.2 303 3.4  87467 1.39 × 10⁻⁶ Ex. 2 99.0 0.8 0.2 304 2.0 152 467 1.06 × 10⁻⁶ Ex. 399.1 0.7 0.2 302 0.5 232 478 1.22 × 10⁻⁶ Ex. 4 98.6 1.2 0.2 305 1.3 181474 1.51 × 10⁻⁶ Ex. 5 97.3 1.9 0.8 304 1.4 186 459 1.40 × 10⁻⁶ Ex. 697.2 1.8 1.0 300 6.7 100 458 1.34 × 10⁻⁶ Ex. 7 Composition of Ex. 6 andliquid — 6.8 120 458 7.08 × 10⁻⁷ chemical permeation inhibitor (100/1 inweight ratio) Com. Ex. 1 97.9 2.1 0 304 2.0 240 477 2.34 × 10⁻⁶

The results in Examples 1 to 6 (in Table 1) show that the permeationamounts of liquid chemical of the fluorine-containing terpolymersmodified by higher perfluoro(vinyl ether) (2) (n=2VE) is reduced by asmuch as at least 30% compared to copolymer of Comparative Example 1.Furthermore, the results of Example 7 show that the permeation amount ofnitric acid was reduced by at least 30% by adding only 1% by weight ofthe fluorine-containing multi-segmented polymer as a liquid chemicalpermeation inhibitor.

In addition, the novel fluorine-containing copolymers obtained in thepresent invention do not show any remarkable lowering of melting pointor decomposition temperature and maintains heat resistance as high asthat of Comparative Example 1. Further, there is no remarkable decreaseof MIT value, which means that excellent flexible resistance ismaintained. Accordingly, the obtained copolymers are most suitable fortubes, pipes, tanks or connectors used for semiconductor productionapparatus.

INDUSTRIAL APPLICABILITY

According to the present invention, novel fluorine-containing copolymersobtained by modification using perfluoro(vinyl ether) having a long sidechain provide improved prevention capability of liquid chemicalpermeation while retaining inherent and excellent heat resistance,stress cracking resistance and processability. Molded articles obtainedfrom the copolymer or the resin composition comprising the copolymer anda liquid chemical permeation inhibitor are suitable as a material to beused in the field of semiconductor production apparatus and the like.

What is claimed is:
 1. A fluorine-containing copolymer comprising 90 to99.4% by mole of a repeating unit derived from tetrafluoroethylene, 0.5to 5% by mole of a repeating unit derived from at least one lowerperfluoro(alkyl vinyl ether) represented by the formula (1):CF₂═CF—O—Rf¹  (1) in which Rf¹ is a perfluoroalkyl group having 2 to 4carbon atoms, and 0.1 to 5% by mole of a repeating unit derived from atleast one higher perfluoro(vinyl ether) represented by the formula (2):CF₂═CF═O—Rf²  (2) in which Rf² is a perfluoro(alkoxy alkyl) group having4 to 17 carbon atoms, wherein the fluorine-containing copolymer has amelt flow rate of 0.1 g/10 minutes to 100 g/10 minutes and melting pointof 290° to 325° C.
 2. The copolymer of claim 1, wherein Rf² in theformula (2) is perfluoro(alkoxy alkyl) group represented by the formula(3): —(CF₂C(CF₃)FO)_(n)—Rf³  (3) in which n is an integer of 1 to 4 andRf³ is a perfluoroalkyl group having 1 to 5 carbon atoms.
 3. Afluorine-containing resin composition comprising 0.1 to 50 parts byweight of a fluorine-containing multi-segmented polymer comprising (A)an amorphous polymer chain segment which comprises atetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer and (B) acrystalline polymer chain segment which comprises 80 to 100% by mole ofa repairing unit derived from tetrafluoroethylene and 0 to 20% by moleof a repairing unit represented by the formula (6): CF₂═CF—Rf⁴  (6) inwhich Rf⁴ is CF₃ or ORf⁵ (Rf⁵ is perfluoroalkyl group having 1 to 5carbon atoms), or an amorphous polymer comprising tetrafluoroethyleneperfluoro(alkyl vinyl ether) copolymer, based on 100 parts by weight ofthe copolymer of claim 1 or
 2. 4. A fluorine-containing resincomposition comprising 0.1 to 50 parts by weight of afluorine-containing multi-segmented polymer comprising (A) an amorphouspolymer chain segment which comprises atetrafluorethylene-perfluoro(alkyl vinyl ether) copolymer and (B) acrystalline polymer chain segment which comprises 80 to 100% by mole ofa repeating unit derived from tetrafluoroethylene and 0 to 20% by moleof a repeating unit represented by the formula (6): CF₂═CF—Rf⁴  (6) inwhich Rf⁴ is CF₃ or ORf⁵ (Rf⁵ is a perfluoroalkyl group having 1 to 5carbon atoms), or an amorphous polymer comprisingtetrafluoroethylene-perfluoro (alkyl vinyl ether) copolymer, based on100 parts by weight of the copolymer of claim
 2. 5. A molded articleobtained by melt-molding the fluorine-containing copolymer of claim 1.6. A molded article obtained by melt-molding the fluorine-containingcopolymer of claim
 2. 7. A molded article obtained by melt-molding thefluorine-containing resin composition of claim
 3. 8. A molded articleobtained by melt-molding the fluorine-containing resin composition ofclaim
 4. 9. The molded article of claim 5, whose permeation amount ofnitric acid is at most 2.0×10⁻⁶ g.cm/cm² after 40 days in a liquidchemical permeation test.
 10. The molded article of claim 6, whosepermeation amount of nitric acid is at most 2.0×10⁻⁶ g.cm/cm² after 40days in a liquid chemical permeation test.
 11. The molded article ofclaim 7, whose permeation amount of nitric acid is at most 2.0×10⁻⁶g.cm/cm² after 40 days in a liquid chemical permeation test.
 12. Themolded article of claim 8, whose permeation amount of nitric acid is atmost 2.0×10⁻⁶ g.cm/cm² after 40 days in a liquid chemical permeationtest.